Areas near rivers and streams are at risk of flooding. To calculate an appropriate insurance premium for risks located in an area prone to flooding, information on the frequency of flooding is required. Flood data maps are available from historical flood events and from hydrological modeling studies for some few countries or portions of countries. Still, for most countries (or portions of countries) flood zones are often not available for the flood return periods (e.g., 50 years, 100 years, 250 years, 500 years, etc.) of interest.
One approach to estimating flood areas and frequencies in the absence of historical data is hydrological modeling. This approach is complicated and time consuming, however, and can require months of computation time to develop an acceptable model for a particular region and/or country.
The present invention takes an alternative approach to traditional methods of estimating flood area and frequency. That approach is based upon a statistical estimation process. Inputs to the statistical process are variables which can be derived from digital terrain models (digitized, topological maps). Digital terrain models are available, or can be readily gathered, from a number of sources.
In one embodiment, the geographic region or country of interest is divided into grid cells. Digitized topological data are inputted for the region and the statistical “model” is used to generate output for each grid cell. The output may take the form of a “1” or “0” to indicate a “flooded” or “not flooded” condition, respectively, for a return period of interest (e.g., between 50 years and 500 years). In this approach, all grid cells having the same value for a return period of 100 years or less, for example, will define the 100 year flood zone.
In certain embodiments of the invention, return periods of 50 years, 100 years, 250 years and 500 years are utilized. Flood zones are defined for each of these return periods. Furthermore, with the invention it is possible to calculate the flood zones for any possible return period between 50 and 500 years. These flood zones are combined with other data and used in the underwriting process to evaluate property risks. That is, an underwriter can use the output of the system and method to determine the probable flooding frequency when underwriting insurance for a particular risk (e.g., a factory).
In certain embodiments of the invention, a model is developed for use in connection with a particular return period, and then used in determination of the probability of a flood occurrence in an alternative return period. For example, a model may be developed to determine the probability of occurrence of a 100-year flood event. Calibration data of good quality are available for multiple regions for the 100-year recurrence interval. For other return periods (for example, the 500-year return period), less data are available. In these embodiments, the 100-year model may be modified to approximate flood events for other return periods.
Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the method as presently perceived.